Luke 11:30

For as Jonas was a sign to the Ninevites As he was by lying three days and three nights in the whale's belly, and then cast on shore alive; which sign, or miracle was wrought to confirm his mission and message, and to engage the Ninevites to give credit to him, and repent, or they might assure themselves they would be utterly destroyed;

so shall also the son of man be to this generation; by lying three days and three nights in the heart of the earth, and then rising again from the dead the third day; and which should be done to confirm the truth of his Messiahship, and to declare him to be the Son of God with power, and to engage persons to believe in him; and to assure that wicked generation, that in case they remained, after such a sign, impenitent and unbelieving, wrath would come upon them to the uttermost; see ( Matthew 12:40 ) .